What is the magnetic dipole moment of an electron revolving in a circular orbit of radius 'r' with a uniform speed 'v'? MCQ with Answer and Explanation
What is the magnetic dipole moment of an electron revolving in a circular orbit of radius 'r' with a uniform speed 'v'?
A. evr
B. evr / 2
C. 2evr
D. e / (vr)
Answer: Option B
Solution (By JKSSB Mock Tests)
Magnetic dipole moment M = Current(I) * Area(A). Current is charge/time: I = e / T. Time period T = 2pir / v. So I = ev / (2pir). The area of the circular orbit is A = pir^2. Therefore, M = [ev / (2pir)] * [pir^2] = evr / 2. This is a standard derivation in modern physics.
In standard AC household supply in India, the frequency of the alternating current is 50 Hz. How many times per second does the current change its direction?
Explanation:
A frequency of 50 Hz means there are 50 complete wave cycles per second. A single complete sinusoidal cycle consists of one positive half-cycle and one negative half-cycle. Therefore, the current reaches zero and reverses its direction exactly twice during each complete cycle. For 50 cycles, the current changes direction 50 * 2 = 100 times per second.
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